A variety of bacteria coexist with the human body, forming bacterial populations which are referred to as normal, or indigenous, bacterial flora. Although pathogens and opportunistic infectious bacteria are present in these normal bacterial flora, when a balance in the bacterial flora is maintained, diseases caused by such bacteria are suppressed, affording a state of health. However, when the balance in the bacterial flora breaks down due to eating habits, the ingestion of antibiotics, stress, aging and the like, the pathogens and opportunistic infectious bacteria increase, leading to illness. Therefore, in order to control illness, it is important not only to suppress pathogens, but also to maintain a balance in the normal bacterial flora by activating non-pathogenic indigenous bacteria.
Of the several hundred species of bacteria that live in the oral cavity, only a few species of bacteria exhibit pathogenicity. These include Porphyromonas gingivalis, an organism that causes periodontal disease, and Streptococcus mutans, an organism that causes dental caries. Most of the other species are normal bacteria which are generally non-pathogenic in the oral cavity, including the following which typically do not exhibit pathogenicity in humans; bacteria of the genus Streptococcus of the Mitis group such as Streptococcus gordonii, Streptococcus mitis and Streptococcus oxalis, bacteria of the genus Veillonella such as Veillonella parvula, and bacteria of the genus Neisseria such as Neisseria subflaba. Therefore, to prevent diseases of the oral cavity, it is important to form and maintain within the mouth a good balance of bacterial flora made up of such normal, non-pathogenic bacteria.
In particular, Mitis group streptococci are indigenous bacteria which are known to play a role in adherence to the tooth plane of the above dental caries and periodontal disease pathogens and to have antibacterial effects (Non-Patent Document 1), whose use as probiotics has also been disclosed (Patent Document 1: WO 2013/021957), and which act to suppress diseases of the oral cavity.
In this connection, the following art has been disclosed: an agent for improving the bacterial flora in the oral cavity and an agent for promoting the growth of indigenous bacteria, which agents contain ganglioside as an effective ingredient (Patent Document 2: JP-A 2005-320275); art which uses caffeine to improve the oral bacterial flora (Patent Document 3: JP-A 2012-77053); and oral compositions which have an antibacterial activity on dental caries-forming bacteria and also have the effect of increasing lactic acid degrading bacteria (Patent Documents 4 and 5: JP-A H08-175946, JP-A H08-175947). However, the advantageous effects of such art have been inadequate.